Telematics units within mobile vehicles provide subscribers with connectivity to a telematics service provider (TSP). The TSP provides subscribers with an array of services ranging from emergency call handling and stolen vehicle recovery to diagnostics monitoring, global navigation system aided position identification, map services, and turn-by-turn navigation assistance. Telematics units are often provisioned and activated at a point of sale when a subscriber purchases a telematics-equipped vehicle. Once provisioned and activated, telematics units can be utilized by a subscriber to obtain telematics services, such as those described herein, from the TSP.
One service provided by a TSP is a Global Navigation Satellite System (GNSS) based navigation service. GNSS is a generic term referring to any of multiple satellite constellation-based global positioning networks including, for example, the Global Positioning System (GPS) constellation. A particular example of a GNSS based navigation service is the provision of turn-by-turn (TBT) directions from a current location of a vehicle or an alternative start location to a specified destination.
A telematics unit equipped with a GNSS receiver can utilize the signals broadcast by GNSS satellites to calculate the coordinated universal time (UTC) with a high degree of accuracy. GNSS satellites continually broadcast signals that, when processed, provide a time at which the signal was transmitted (as measured by the satellites' onboard clocks) and a location at which the signal was transmitted. The telematics unit can use the information provided by the signals to calculate the UTC with a high degree of accuracy and thereby maintain a highly accurate on-board clock.